In the recent decades, increased focus has been directed to the exploitation of renewable energy sources.
Wave energy is a renewable energy resource that for one part may be created by large storms hundreds of kilometers offshore that generate and transmit huge amounts of energy that travels great distances via swell, and for another part may be created by local influences, such as local seas that are generated by local winds. Wave energy is a genuinely renewable energy source and distinct from tidal energy. Wave energy plants can be configured to exploit wave energy stemming from both remotely generated swell and local seas.
Wave energy as a renewable energy source has a number of advantages. One advantage is the high power density of wave energy that suggests it has the capacity to become the lowest cost renewable energy source. A further advantage is the predictability of wave energy: unlike solar and wind, wave energy levels can be predicted many days in advance, making it less challenging to integrate wave energy with national power supplies.
However, while being predictable, the waves carrying that energy are typically highly irregular, wherein the wave climate at a given location observed over a certain period of time, e.g. over one year, comprises a statistical distribution of wavelengths, heights and directions. Depending on the local conditions of a deployment site of a wave energy plant, the observed waves may be the result of a superposition from a number of different sources. The resulting wave fields may vary from essentially parallel wave fronts coming from a well-defined direction (referred to as 2D-waves), to being highly complex with numerous different directional components (referred to as 3D-waves).
Furthermore, marine environments are particularly harsh environments, where a need for frequent maintenance and repair can seriously affect the operational up-time of the wave energy plant for energy production.
A major challenge of the exploitation of wave energy is therefore to maximize energy production year round, including increasing the efficiency of the energy absorption, harvesting energy under varying wave conditions, maximizing production up-time of a wave energy plant and producing useful energy at a competitive cost level.
A wave energy plant using absorbers of the front pivot type is disclosed in DK 174 463 B1 where a plurality of front pivot absorber elements are pivotally attached to a submerged platform to swing around a horizontal pivot axis arranged at the front of the absorber element. Under operation, incoming waves travel from the front end towards a rear end of the absorber element interacting with it to absorb both kinetic and potential energy from the waves. The resulting motion of the absorber element with respect to the platform frame is exploited by a hydraulic power take-off system. The disclosed absorber element comprises a floating body with a closed top and an open bottom and may further be divided into cells with perforated walls acting as a flow resistance for water flowing into and out of the floating body so as to improve the wave tracking properties of the absorber. However, no further indications are given on how to provide and configure an absorber that is efficient over a broad wave spectrum as required for practical applications.